Suctioning IS NOT the recommended field treatment [unless you are more than 24-48 hours from help---even then, its affectiveness is +/-]. The reason is that the average dayhiker was butchering his own leg and coming close to dying from blood loss, starving the tissues of blood and losing the extremity, or spreading the venom even further into the surrounding tissues.
Nowadays its rest-light tourniquet-have someone go for help. Or hike out after the venom has had time to settle in the tissues[about 20-30 min.], so that the venom doesn't race directly into your bloodstream.

The "recommended" field treatment seems to change every 2-3 years, so it largely depends on who and when you ask.

NPSDs are controversial (as are tourniquets and pressure bands), in the sense that there is on-going debate over their efficacy. (The conclusions of the 2003 study by Alberts, Shalit, and LoGalbo which found NPSDs to be of minimal efficacy, and which is usually cited as the reason for the negative evaluation, has been criticized on methodological grounds.) Pick four experts at random and ask about NPSDs, and you're likely to get 5 opinions.